A liquid crystal display is a display device in which a liquid crystal composition is used for display. The liquid crystal display is used as a display device for various machines, in particular, as an information display device or image display device.
The liquid crystal display shows an image by locally transmitting or blocking light using a liquid crystal panel in accordance with voltage application. Accordingly, to show an image on the liquid crystal display, a backlight is needed for a back surface of a liquid crystal panel. Conventionally, a cold cathode tube is used for such a backlight. In recent years, there are circumstances in which light emitting diodes (LEDs) are used instead of cold cathode tubes, for the reasons of having long service life, good color development, and the like.
Meanwhile, in recent years, nano-sized phosphors using quantum dots have been commercialized mainly by venture companies overseas. Quantum dots are luminescent semiconductor nano-particles and have a diameter in a range of 1 to 20 nm. The unique optical properties and electronic properties of the quantum dots are being utilized in many applications such as flat panel displays and illumination (decorative lighting) with a wide variety of colors, in addition to fluorescent imaging applications in the fields of biology and medical diagnosis.
White LED technology, which plays a supremely important role in displays, generally uses a method of exciting cerium-doped yttrium-aluminum-garnet (YAG-Ce) phosphors for down conversion, by means of a blue (450 nm) LED chip. When the blue light of the LED becomes admixed with the yellow light generated from the YAG phosphors with a wide wavelength range, white light is created. However, this white light commonly is somewhat bluish and therefore is taken to be a “cold” white or “cool” white.
The quantum dots exhibit a wide excitation spectrum and have high quantum efficiency and thus can be used as LED down conversion phosphors. Furthermore, the quantum dots can have an emission wavelength fully adjusted over the entire visible region by only altering the dot size or the type of the semiconductor material. Therefore, it is said that the quantum dots have the possibility of creating substantially any color, in particular, warm whites that are strongly desired in the illumination industry. In addition, combinations of three types of dots having emission wavelengths corresponding to red, green, and blue enable white lights having different color rendering indices to be obtained. Thus, a display provided with a backlight using quantum dots can improve color hue and can express up to 65% of the colors that can be distinguished by a person, without increasing the thickness, power consumption, costs, or manufacturing processes more than those of a conventional liquid crystal display.
The backlight is an optical instrument obtained by diffusing quantum dots having an emission spectrum of red or green into a film and sealing (covering) two main surfaces of the film with a barrier film or a lamination of barrier films, and the edge portions, as well as the main surfaces, are also sealed depending on a case.
Furthermore, it is suggested in PTL 1 that a layer having phosphors is inserted between barrier films to suppress degradation of the phosphors. Furthermore, it is suggested in PTL 2 that an organic EL device is coated with a gas barrier film to ensure the reliability of the organic EL device.